MY01 WRX. Standard car, standard wheels.

The reason I ask is because I've got 225/45 R17's on, not the 215's that come as standard.

I thought the correct pressures might differ slightly?

Thanks

<Russ>

 

Would have thought it would be the same

 

Tyre pressures relate to the weight of the car, not the wheel/tyre size. Stick to whatever's in the handbook, or a little either side (1-3lb) depending on prefered handling. A little harder if you like it direct but skittish, a little softer if you like it grippy but slightly wallowy. I like the front at 30 with the back at 33 so it grips well on turn-in but can snap out into oversteer if provoked

 

I always thought the rears should be less than the front to kill the understeer?

PeteS

 

No, the rears are usually softer as there is less weight over them. The fronts support the engine, 'box, rads, aircon, steering etc. The rears have a (usually) empty boot and (usually) no back seat passengers. A softer tyre will grip more as the tread can form to the road surface easier. Hard tyres at high pressure will easilly break loose and skid, being less able to roll the structure of the tyre during cornering. Hard tyres wear in the centre, soft on the outside edges. Softer tyres will also create more rolling resistance affecting fuel economy and can be dangerous if used at high speed for a prolonged time, as the extra movement in the tyre wall can generate excess heat leading to softening of the walls or blowouts.

 

That's something of a contradiction

 

A personal contradiction....
....as I said, I like the front to bite in on turn-in and the back to be available for hooligan-ness should I want it

 

Personally I like 33-34 at the front and 31-32 at the back. Does vary a little depending on what tyre you have fitted, how many people in the car etc.

What I find is the best way to set them "by trial and error" is to start slightly low, take it out and corner fast round something fairly tight e.g. a roundabout. Keep increasing the pressures slowly and repeat the test. As soon as the tyres start squealing more easily, they are too hard, so go back to the previous setting. Only semi-scientific, but generally works quite well with a little practice

Having the fronts a little too soft IMHO might give decent grip, but softens the steering response too much hence making it less pleasant on turn in. However, as mentioned above, different people prefer different things.

 

Agree with what you say hades, but I have adjustable damping, so I tighten that up to get the steering back in line and let the tyres dig in. Seems to work, especially for getting the back out with little provokation